1. Field of the Invention
The present invention generally relates to keyboards, and more particularly to a keyboard used for data entry in electronic devices.
2. Description of the Prior Art
Keyboards having a plurality of switching elements are used to transfer information based on the intents of operators to computers or other electronic devices. Recently, with the spread of OA (Office Automation) devices, it has been desired to improve the operationability of keyboards.
Generally, keyboards have a plurality of switching elements, each element including a switch member, a keytop and an electronic circuit. The switch member includes an electric contact, which completes or breaks the electric circuit. The keytop receives a depression force by the operator and transfers it to the switch member. The electric circuit generates a code of a character or symbol corresponding to the keytop depressed by the operator, and transfers it to a CPU (Central Processing Unit).
Switch member types include a lead switch, a mechanical switch, a membrane switch or a conductive rubber switch. Currently, the membrane switch is most widely used.
FIGS. 1A, 1B and 1C illustrate the structure of a conventional membrane switch. The membrane switch 10 includes an upper sheet 11, a spacer 12, and a lower sheet 13. The upper sheet 11 and the lower sheet 13 respectively have films 14a and 14b made of polyester. Circuit patterns 15a and 15b and contacts 16a and 16b are formed on the films 14a and 14b by ink containing Ag (silver) or C (carbon). As shown in FIG. 1B, a spacer 12 is sandwiched between the films 14a and 14b, and has an opening located at a contact area where the contacts 16a and 16b face each other. As shown in FIG. 1C, the upper sheet 11 is depressed and the upper contact 16a comes into contact with the contact 16b. Thereby, the switching element is turned ON.
FIG. 2 shows a conventional keytop mechanism 20, which is made up of support panel 21, a housing 22, a slider 23, a keytop 24, and two springs 25 and 26. The support panel 21 is formed with a metal plate such as iron. The housing 22 is provided on the upper surface of the membrane switch 10 formed on the support panel 21. The slider 23 is inserted into the housing 22. The keytop 24 drives the slider 23. The springs 25 and 26 are arranged outside and inside of the housing 22, respectively, and cause the keytop 24 to return to the original position at which the switching element is OFF.
Using the two springs 25 and 26, it is possible to turn the switching element ON before the keytop 24 is completely depressed. In this case, a comfortable feel to the key operation can be obtained. The slidable distance of the slider 23 is defined as the stroke length. Normally, a stroke length of 3-4 mm is said to provide a comfortable feel to key operation. More particularly, when the keytop 24 is pushed down, the spring 26 is pressed against the membrane switch 10. The contact 16a comes into contact with the contact 16b when the keytop 24 reaches a suitable position and before the keytop 24 is completely depressed, that is, before the keytop 24 is pushed down to the deepest position.
A description of the electric circuit of the keyboard will be omitted because it is not directly concerned with the present invention.
There are many arrangements of keys. In Japan, several "kana"-key arrangements have been used. For example, the JIS (Japanese Industrial Standard) and the new JIS prescribe "Kana"-key arrangements. A thumb shift keyboard proposed by Fujitsu Limited has a "kana"-key arrangement. The so-called QWERTY arrangement is widely used as an alphanumeric key arrangement.
FIGS. 3A and 3B illustrate the above-mentioned thumb shift keyboard 30. The left area with respect to a center line 31 has character keys and digit keys arranged in four rows and five columns, and special keys (sometimes called function keys) arranged in the fifth row including the "CTRL" key and the "ALT" key. The right area with respect to the center line 31 has character keys and digit keys arranged in four rows and five columns, and special keys and a space key arranged in the fifth row. Further, two function keys are arranged in the sixth (lowermost) row. The keys arranged in a right-hand area 33 indicated by hatching are touched by the fingers of the right hand.
FIG. 4 illustrates how the keyboard 30 shown in FIGS. 3A and 3B is operated by the operator. The fingers of the right and left hands are located at the home position of the keyboard 30. Generally, the well-experienced operator can correctly operate the keys in the right and left hand areas without seeing the labels on the keytops. In light of the above, the right and left hand areas are called blind-touch areas. At the home position, the index finger and the little finger of the left hand are placed on the "F" and "A" keys in the left-hand area, respectively, and the index finger and the little finger of the right hand are placed on the "J" and ";" keys in the right-hand area. Generally, projections are formed on the keytops "F", "A", ";" and "J" in order to distinguish these keys from the other keys.
The keytops are depressed by the corresponding fingers. The "space" key and the "shift" keys are operated with the side portions of the thumb s. The heights of the keytops are designed to allow depression of the keytops by the tips of the fingers without difficulty. More particularly, the envelope connecting the keytops located between the first and sixth rows is curved so that the heights of the keytops gradually increase with respect to a base height (for example, that of the sixth row) increase from the side of the operator. There are known a slope type, a step type and a sculpture type of envelope arrangements. The keytops located in the same rows have the same height as each other.
The applicants are aware of the following documents. Japanese Laid-Open Utility Model Publication No. 58-133843 discloses a keyboard having special keys added to the conventional key arrangement. The cross-sections of the special keys are curved and operated with the side portions of the palms of the hands. The special keys are used to switch the operation modes.
Japanese Laid-Open Patent Publication No. 59-67069 discloses a keyboard having a special key added to the conventional key arrangement. The special key can be operated by the side portion of the palm of the left or right hand in a state in which the fingers are located at the home position.
U.S. Pat. No. 5,017,030 discloses a newly designed keyboard having keys operable with the fingers of the hands kept open. It is to be noted that the keyboards disclosed in the above documents are not conventional, and the components, such as a housing or membrane sheet, must be newly designed.
U.S. Pat. No. 4,512,092 discloses replacement labels for a keyboard in which labels on the keytops are easily replaceable.
Japanese Laid-open Patent Publication No. 62-22129 discloses a keyboard having special keytops higher than other keytops. The keyboard disclosed in this document is intended to realize key operation in a state in which the wrists can at rest. The special keytops are arranged at the thumb sides inside pedestals on which the writes are rest. Further, the special keys are disposed at a level other than levels of the other keys, and are operated by chips of the thumb fingers.
The conventional keyboards, such as thumb shift keyboards, have some difficulties in key operation, particularly for programming and producing documents or files. Nowadays, programming or making documents or files is carried out using an editor. Many available editors use combinations of a special key (for example, "CTRL" (control) key) and alphanumeric keys. These key combinations make it possible to input the same operations or instructions as those specified by special keys located outside of the blind-touch areas.
For example, when an alphanumeric key is operated while the "CTRL" key is being depressed, the following operations on movement of the cursor are input: (CTRL)+E=.uparw., (CTRL)+S=.rarw., (CTRL)+X=.dwnarw., (CTRL)+D=.fwdarw.. Further, the combination of the "CTRL" key and the "G" key specifies a delete function, and the combination of the "CTRL" key and the "C" key specifies a scroll.
FIGS. 5 and 6 show how the keyboard (thumb shift keyboard) is operated in the above-described manner. More particularly, FIGS. 5 and 6 show how the "CTRL" key located at the lower left corner and the "D" key are operated. In FIG. 5, the "CTRL" key is operated by the index finger of the left hand, and the "D" key is operated by the index finger of the right hand. In FIG. 6, the "CTRL" key and the "D" key are respectively operated by the little and index fingers of the left hand. However, the operations shown in FIGS. 5 and 6 are not natural and easy.